/Engine/Source/Runtime/SlateCore/Public/Widgets/SBoxPanel.h
Called when Slate detects that a widget started to be dragged. Usage: A widget can ask Slate to detect a drag. OnMouseDown() reply withFReply::Handled().DetectDrag( SharedThis(this) ). Slate will either send anOnDragDetected()event or do nothing. If the user releases a mouse button or leaves the widget before a drag is triggered (maybe user started at the very edge) then no event will be sent.
virtual [FReply](API\Runtime\SlateCore\Input\FReply) OnDragDetected ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & MyGeometry, const [FPointerEvent](API\Runtime\SlateCore\Input\FPointerEvent) & MouseEvent )